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    <title>Document</title>
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<script>
      //创建数组并赋值
      let arr=[23,566,21,542,78];
      console.log(arr[2]); //21
      let arr2=['tom',34.4,true,,,,];
      console.log(arr2[4]);
      arr2[4]=null;
      console.log(arr2[4]);
      console.log('------------');
      //遍历数组
      //console.log(arr);
      console.log(arr.length); //获取数组长度
      /*for(let i=0;i<arr.length;i++){
        console.log(arr[i]);
      }*/
      //1.找出数组score中的最大值，并算出这个数组的平均数
      //score=[89,67,59,90,54,77,83,88,88.5,43,10,68]
      let score=[89,67,59,90,54,77,83,88,88.5,43,10,68];
      let max=score[0];
      let sum=0;
      console.log(score.length);
      for(let i=0;i<score.length;i++){
        if(score[i]>max){
            max=score[i];
        }
        sum+=score[i];
      }
      let avg=sum/score.length;
      console.log('最大值是：'+max);
      console.log('平均分数为：'+avg);
      console.log('------------');
      score[1000]=98;
      console.log(score[1000]);
      console.log(score.length);
      for(let i=0;i<score.length;i++){
        console.log(score[i]);
      }
      delete score[1000];
      console.log(score[1000]);
</script>
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